Example: Calling a Provider Method
You can use the procedure and code examples in this topic to create a complete WMI client application that performs COM initialization, connects to WMI on the local computer, calls a provider method, and then cleans up. The Win32_Process::Create method is used to start Notepad.exe in a new process.
The following procedure is used to execute the WMI application. Steps 1 through 5 contain all of the steps needed to set up and connect to WMI, and 6 is where the provider method is called.
To call a provider method
Initialize COM parameters with a call to CoInitializeEx.
For more information, see Initializing COM for a WMI Application.
Initialize COM process security by calling CoInitializeSecurity.
For more information, see Setting the Default Process Security Level Using C++.
Obtain the initial locator to WMI by calling CoCreateInstance.
For more information, see Creating a Connection to a WMI Namespace.
Obtain a pointer to IWbemServices for the root\cimv2 namespace on the local computer by calling IWbemLocator::ConnectServer. To connect to a remote computer, see Example: Getting WMI Data from a Remote Computer.
For more information, see Creating a Connection to a WMI Namespace.
Set IWbemServices proxy security so the WMI service can impersonate the client by calling CoSetProxyBlanket.
For more information, see Setting the Security Levels on a WMI Connection.
Use the IWbemServices pointer to make requests to WMI. This example uses IWbemServices::ExecMethod to call the provider method Win32_Process::Create.
For more information about making requests to WMI, see Manipulating Class and Instance Information and Calling a Method.
If the provider method has any in-parameters or out-parameters, then values of the parameters must be given to IWbemClassObject pointers. For in-parameters, you must spawn an instance of the in-parameter definitions, and then set the values of these new instances. The Win32_Process::Create method requires a value for the CommandLine in-parameter to execute properly.
The following code example creates an IWbemClassObject pointer, spawns a new instance of the Win32_Process::Create in-parameter definitions, and then sets the value of the CommandLine in-parameter to Notepad.exe.
// Set up to call the Win32_Process::Create method BSTR MethodName = SysAllocString(L"Create"); BSTR ClassName = SysAllocString(L"Win32_Process"); IWbemClassObject* pClass = NULL; hres = pSvc->GetObject(ClassName, 0, NULL, &pClass, NULL); IWbemClassObject* pInParamsDefinition = NULL; hres = pClass->GetMethod(MethodName, 0, &pInParamsDefinition, NULL); IWbemClassObject* pClassInstance = NULL; hres = pInParamsDefinition->SpawnInstance(0, &pClassInstance); // Create the values for the in-parameters VARIANT varCommand; varCommand.vt = VT_BSTR; varCommand.bstrVal = _bstr_t(L"notepad.exe"); // Store the value for the in-parameters hres = pClassInstance->Put(L"CommandLine", 0, &varCommand, 0); wprintf(L"The command is: %s\n", V_BSTR(&varCommand));The following code example shows how the Win32_Process::Create method out-parameters are given to an IWbemClassObject pointer. The out-parameter value is obtained with the IWbemClassObject::Get method and stored in a VARIANT variable so that it can be displayed to the user.
// Execute Method IWbemClassObject* pOutParams = NULL; hres = pSvc->ExecMethod(ClassName, MethodName, 0, NULL, pClassInstance, &pOutParams, NULL); VARIANT varReturnValue; hres = pOutParams->Get(_bstr_t(L"ReturnValue"), 0, &varReturnValue, NULL, 0);
The following code example shows how to call a provider method using WMI.
#define _WIN32_DCOM
#include <iostream>
using namespace std;
#include <comdef.h>
#include <Wbemidl.h>
#pragma comment(lib, "wbemuuid.lib")
int main(int iArgCnt, char ** argv)
{
HRESULT hres;
// Step 1: --------------------------------------------------
// Initialize COM. ------------------------------------------
hres = CoInitializeEx(0, COINIT_MULTITHREADED);
if (FAILED(hres))
{
cout << "Failed to initialize COM library. Error code = 0x"
<< hex << hres << endl;
return 1; // Program has failed.
}
// Step 2: --------------------------------------------------
// Set general COM security levels --------------------------
hres = CoInitializeSecurity(
NULL,
-1, // COM negotiates service
NULL, // Authentication services
NULL, // Reserved
RPC_C_AUTHN_LEVEL_DEFAULT, // Default authentication
RPC_C_IMP_LEVEL_IMPERSONATE, // Default Impersonation
NULL, // Authentication info
EOAC_NONE, // Additional capabilities
NULL // Reserved
);
if (FAILED(hres))
{
cout << "Failed to initialize security. Error code = 0x"
<< hex << hres << endl;
CoUninitialize();
return 1; // Program has failed.
}
// Step 3: ---------------------------------------------------
// Obtain the initial locator to WMI -------------------------
IWbemLocator *pLoc = NULL;
hres = CoCreateInstance(
CLSID_WbemLocator,
0,
CLSCTX_INPROC_SERVER,
IID_IWbemLocator, (LPVOID *) &pLoc);
if (FAILED(hres))
{
cout << "Failed to create IWbemLocator object. "
<< "Err code = 0x"
<< hex << hres << endl;
CoUninitialize();
return 1; // Program has failed.
}
// Step 4: ---------------------------------------------------
// Connect to WMI through the IWbemLocator::ConnectServer method
IWbemServices *pSvc = NULL;
// Connect to the local root\cimv2 namespace
// and obtain pointer pSvc to make IWbemServices calls.
hres = pLoc->ConnectServer(
_bstr_t(L"ROOT\\CIMV2"),
NULL,
NULL,
0,
NULL,
0,
0,
&pSvc
);
if (FAILED(hres))
{
cout << "Could not connect. Error code = 0x"
<< hex << hres << endl;
pLoc->Release();
CoUninitialize();
return 1; // Program has failed.
}
cout << "Connected to ROOT\\CIMV2 WMI namespace" << endl;
// Step 5: --------------------------------------------------
// Set security levels for the proxy ------------------------
hres = CoSetProxyBlanket(
pSvc, // Indicates the proxy to set
RPC_C_AUTHN_WINNT, // RPC_C_AUTHN_xxx
RPC_C_AUTHZ_NONE, // RPC_C_AUTHZ_xxx
NULL, // Server principal name
RPC_C_AUTHN_LEVEL_CALL, // RPC_C_AUTHN_LEVEL_xxx
RPC_C_IMP_LEVEL_IMPERSONATE, // RPC_C_IMP_LEVEL_xxx
NULL, // client identity
EOAC_NONE // proxy capabilities
);
if (FAILED(hres))
{
cout << "Could not set proxy blanket. Error code = 0x"
<< hex << hres << endl;
pSvc->Release();
pLoc->Release();
CoUninitialize();
return 1; // Program has failed.
}
// Step 6: --------------------------------------------------
// Use the IWbemServices pointer to make requests of WMI ----
// set up to call the Win32_Process::Create method
BSTR MethodName = SysAllocString(L"Create");
BSTR ClassName = SysAllocString(L"Win32_Process");
IWbemClassObject* pClass = NULL;
hres = pSvc->GetObject(ClassName, 0, NULL, &pClass, NULL);
IWbemClassObject* pInParamsDefinition = NULL;
hres = pClass->GetMethod(MethodName, 0,
&pInParamsDefinition, NULL);
IWbemClassObject* pClassInstance = NULL;
hres = pInParamsDefinition->SpawnInstance(0, &pClassInstance);
// Create the values for the in parameters
VARIANT varCommand;
varCommand.vt = VT_BSTR;
varCommand.bstrVal = _bstr_t(L"notepad.exe");
// Store the value for the in parameters
hres = pClassInstance->Put(L"CommandLine", 0,
&varCommand, 0);
wprintf(L"The command is: %s\n", V_BSTR(&varCommand));
// Execute Method
IWbemClassObject* pOutParams = NULL;
hres = pSvc->ExecMethod(ClassName, MethodName, 0,
NULL, pClassInstance, &pOutParams, NULL);
if (FAILED(hres))
{
cout << "Could not execute method. Error code = 0x"
<< hex << hres << endl;
VariantClear(&varCommand);
SysFreeString(ClassName);
SysFreeString(MethodName);
pClass->Release();
pClassInstance->Release();
pInParamsDefinition->Release();
pOutParams->Release();
pSvc->Release();
pLoc->Release();
CoUninitialize();
return 1; // Program has failed.
}
// To see what the method returned,
// use the following code. The return value will
// be in &varReturnValue
VARIANT varReturnValue;
hres = pOutParams->Get(_bstr_t(L"ReturnValue"), 0,
&varReturnValue, NULL, 0);
// Clean up
//--------------------------
VariantClear(&varCommand);
VariantClear(&varReturnValue);
SysFreeString(ClassName);
SysFreeString(MethodName);
pClass->Release();
pClassInstance->Release();
pInParamsDefinition->Release();
pOutParams->Release();
pLoc->Release();
pSvc->Release();
CoUninitialize();
return 0;
}
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